To employ a plug to affect blockage of a normally open flow passage for repair purposes has been known in the prior art in connection with many types of fluid flow systems. Examples of expansible plugs or dams of the prior art may be found in U.S. Pat. Nos. 2,843,154; 3,834,422; and 4,518,015. From these concepts, which are generally applicable to flow passageways, nozzle plugs for steam generators of conventional nuclear power generating systems have developed. Examples of such a nozzle plug for effecting a temporary blockage of a passage into or out of a nuclear power system steam generator will be found in U.S. Pat. No. 4,482,076 to Timothy H. Wentzell, assigned to Combustion Engineering, Inc., the assignee of the instant invention and U.S. patent application Ser. No. 128,235, filed Dec. 3, 1987, by John T. Lewis and Harold R. Zumbrun, also assigned to Combustion Engineering, Inc., the assignee of the instant invention.
Periodically, there arises a need to conduct maintenance on, and to effect minor reports of, the internal components of the steam generator. To accomplish such tasks, it is necessary for one or more persons to physically enter the steam generator. Ingress and egress to and from the steam generator by such persons is accomplished through suitable means such as, for example, an access port or manway. While such persons are working in the steam generator, it is desirable that a blockage of the inlet and outlet nozzle of the steam generator be effected to ensure that there will be no fluid flow through the steam generator which might physically imperil the people working therein.
One such design of a nozzle plug for a nuclear steam generator is disclosed in the U.S. Pat. No. 4,482,076 mentioned above. In that design, a plurality of plate sections or segments are assembled within the steam generator to form the plug or nozzle dam. U.S. Pat. No. 4,483,457 to Schukei and Tade discloses a variation from the Wentzell patent in that it provides for the segments of the nozzle dams to be hinged together.
Both of these patents teach dams which rely upon inflatable seals that require a regulated air supply. See also U.S. Pat. No. 4,566,714. The air supply lines go through the manway and make entry and exit difficult for workers. In addition, there are situations where the hoses and fittings are inadvertently damaged, and since the system remains connected to the air supply lines to maintain pressure on the diaphragm and within the inflatable seal around the periphery of the diaphragm, this can cause leakage.
Moreover, in order to inflate the diaphragm and seals, air lines must be connected from the diaphragm to a regulated air supply outside the primary head of the heat exchanger. The obstruction caused by the air lines in the manway slows down the work effort in the high radiation area of the primary head cavity and is, therefore, extremely detrimental. The removal of the air lines from the work area in the primary head cavity and the manway provides a much more efficient work area. The nozzle dam system can be greatly simplified if there is an elimination of the prior art air supply system for sealing nozzle dams.